Supercritical CO ₂ Extraction of <i>Nicotiana tabacum</i> Oil: Process Optimization and Characterization of Phenolic and Antioxidant Compounds

Supercritical carbon dioxide (SC–CO2) extraction has emerged as an environmentally friendly technique for recovering bioactive compounds from plant matrices. In this study, the extraction of oil and antioxidant compounds from Nicotiana tabacum was investigated using a co-solvent-assisted SC–CO2 process. The effects of pressure (20–30 MPa), temperature (40–60 °C), and ethanol co-solvent concentration (4–8%) on oil yield, total phenolic content (TPC), total flavonoid content (TFC), and antioxidant activity (AA) were evaluated using a Box–Behnken design (BBD) combined with response surface methodology. The experimental results showed that oil yield ranged from 5.21 to 8.56%, while TPC, TFC, and AA varied between 33.72–95.43 mg/100 g, 29.54–79.21 mg/100 g, and 62.72–92.83%, respectively. Statistical analysis confirmed that the quadratic models were significant for all responses, with coefficients of determination (R2) between 0.8450 and 0.9915. Pressure was identified as the dominant factor influencing phenolic, flavonoid, and antioxidant recovery, whereas ethanol co-solvent concentration significantly enhanced oil yield through polarity modification of the supercritical solvent. Response surface analysis further demonstrated the synergistic effects of pressure and ethanol in improving extraction performance. Numerical optimization predicted the optimal extraction conditions at 20 MPa pressure, 47.8 °C temperature, and 5.96% ethanol, yielding 7.21% oil, 91.60 mg/g TPC, 77.33 mg/g TFC, and 81.88% antioxidant activity. The findings highlight the importance of co-solvent-assisted SC–CO2 extraction for enhancing the recovery of antioxidant-rich tobacco oil, providing a sustainable and efficient approach for valorizing tobacco-derived bioactive compounds.